A MURINE MODEL OF ANTIBODY-MEDIATED HYPERACUTE REJECTION BY GALACTOSE-ALPHA(1,3)GALACTOSE ANTIBODIES IN GAL O O MICE/

Background. In pig-to-primate/human xenografts, hyperacute rejection o f primarily vascularized organs usually occurs in 10-60 min and is due to the reaction of the recipients' natural antibodies with antigens e xpressed on the donor endothelium, the fixation of complement, and ult imately vascular stasis and hemorrhage. Surprisingly, the major target of the natural antibodies is the disaccharide galactose-alpha(1,3)gal actose (Gala(1,3)Gal), which is found on many different molecules in p ig tissues and reacts with naturally occurring human anti-pig IgM and IgG antibodies, There are a number of strategies to remove/block/alter Gal alpha(1,3)Gal expression in pig tissues, all of which involve the expression of transgenes in pigs. To overcome the difficulty of precl inical studies using primates, we describe a model of hyperacute rejec tion of heart transplants to Gal o/o mice, which are similar to humans in that they have anti-Gal alpha(1,3)Gal antibodies. Methods. Gal o/o mice received skin or heart grafts from Gal(+) mice or rats, and addi tional antibody and complement were provided; hyperacute rejection was monitored by observation and histology, Results. Gal alpha(1,3)Gal(+) mouse tissues (skin or heart) are not rejected by Gal o/o mice. This was not unexpected, as mice do not utilize alloantibody/complement sys tems satisfactorily in experimental transplantation studies, However, with the addition of anti-Gal alpha(1,3)Gal antibody and complement, h yperacute rejection of hearts can occur in 10-20 min; it is mediated b y IgM, not IgG, antibodies and leads predominantly to tissue hemorrhag e. Conclusion. Gal alpha(1,3)Gal antigen modification by expression of the H transferase cDNA leads to ''indefinite'' survival (>120 min) an d no hyperacute rejection, which shows that this model is suitable for the study of antibody-mediated rejection of relevance to pig-to-human xenografts.